Why are water storage tanks usually built on towers or hilltops? ?

Because when you open the faucet, you want the water to
rush out with pressure, not just dribble or ooze out.  The
water has to be supplied to the user with pressure.  Either
you supply it from a height, or else you'll need to use pumps
to make the pressure.

The charge of an ion with 55 protons and 52 electrons is +3. the reason is because protons are positive, and there are three more than the amount of negative electrons.